AIM: Pre-eruptive intra-coronal radiolucency (PEIR) describes a
radiolucent lesion located in the coronal dentine, just beneath the
enamel-dentine junction of unerupted teeth. The prevalence of this
lesion varies depending on the type and quality of radiographic exposure
and age of patients used for assessment. The aetiology of pre-eruptive
intra-coronal radiolucent lesions is not fully understood, but published
clinical and histological evidence suggest that these lesions are
resorptive in nature. Issues around the diagnosis, treatment planning
and clinical management of this lesion are explored using previously
unreported cases. CASE REPORTS: Case 1: A ten-year-old girl attended for
a routine check-up. An intra-coronal radiolucency in the unerupted lower
right second premolar was an incidental finding on orthopantomograph
(OPT). The tooth erupted and removal of enamel revealed a space filled
with soft red tissue, unlike carious dentine in appearance. The tooth
was restored with an indirect pulp cap, resin modified glass ionomer
base and composite resin. Tissue from the lesion was removed for
histopathological investigation. Root development continued to
completion and the tooth remained asymptomatic and vital. Case 2: A
six-year-old girl attended for her first dental visit. An intra-coronal
radiolucency in a lower right first permanent molar was noted on
baseline bitewing radiographs. The lesion was monitored and fissured
sealed upon eruption. The lesion was monitored annually
radiographically. The tooth remained symptom free for 5 years. The
patient presented on an emergency basis having fractured the
distolingual cusp overlying the lesion. There was no pain and the tooth
was vital. The softened dentine was removed and the tooth was restored
using a preformed metal crown. Case 3: A 12-year-old girl was referred
for restoration of mandibular left second permanent molar. Clinically
there was extensive occlusal destruction. Review of a previous OPT
showed that an intra-coronal radiolucency was present in tooth 37 at
least one year prior to its eruption. The large mass of coronal soft
tissue was removed, the remaining enamel shell was deemed to be
unrestoreable and the tooth was extracted. The patient was referred back
to an orthodontist for completion of orthodontic treatment. CONCLUSION:
Early detection and classification of the PEIR lesion allows an array of
individualised treatments to be provided for successful outcome.

Radiographs occasionally reveal unusual intra-coronal
radiolucencies in the dentine of unerupted teeth. In earlier literature,
these lesions were confused with caries and incorrectly recorded as
occult, hidden or pre-eruptive caries. Currently the accepted term is
pre-eruptive intra-coronal radiolucency/ resorption (PEIR). This term
describes an abnormal, well-circumscribed, radiolucent area within the
coronal dentine of unerupted teeth [Seow, 2000; Ozden and Acikgoz,
2009]. Lesions are usually located on the central or mesial occlusal
portion of the crown close to the amelodentinal junction and extend to
various depths of dentine but rarely involve the pulp. The clinical
crown appears intact.

PEIR can be diagnosed if there is radiographic evidence that the
lesion was present pre-eruptively. Table 1 summarises the current
prevalence data obtained from using bitewing (BW) radiographs [Seow et
al., 1999a] and orthopantomographs (OPT) [Seow et al., 1999b; Nik and
Rahman, 2003; Ozden and Acikgoz, 2009]. There are lists of previously
published case reports [Seow, 2000; Ozden and Acikgoz, 2009] outlining
over 70 affected teeth. Table 2 includes the three cases presented here
and additional reports published since 2004. It is evident that PEIR
most commonly affects a single tooth but multiple teeth can be affected
[Walton, 1980; Seow, 1998; Hata et al., 2007]. The most commonly
affected teeth are molars and premolars, although other tooth types have
been reported [Rankow et al., 1986; Hata et al., 2007]. There has been
only one report of PEIR in the primary dentition [Seow and Hackley,
1996], however this case presented unconventionally as an acute
infection shortly after eruption of the second primary molar and
resorption was shown histopathologically in the extracted tooth.

Various aetiologies of pre-eruptive intra-coronal radiolucencies
have been suggested over the years, originally proposed by Skillen
[1941]. Chronic periapical inflammation of the preceding primary tooth
was one of the first theories postulated [Muhler, 1957], but the
majority of teeth affected do not have a primary precursor. Dental
caries is not likely, as infection with cariogenic microorganisms has
not been shown in unerupted teeth [Davidovich, 2005]. It has been
suggested that the lesion arises when certain sections of the tooth fail
to mineralise properly during development. However, Seow and Hackley
demonstrated that the radiolucency became evident after crown
development is complete. They inferred that the lesion could not be the
result of an intrinsic disturbance of mineralisation.

It is widely accepted now that the process in PEIR is one of
resorption. Markers representative of resorption such as multinucleated
giant cells, osteoclasts and chronic inflammatory cells have been
described in the histopathology reports in numerous case reports
[Blackwood, 1958; Grundy et al., 1984; Brooks, 1988; Seow and Hackley,
1996]. The triggering factors are as yet unknown. The classification of
tooth resorption in general, is not well understood and considerable
challenges exist when trying to determine aetiology and predict clinical
behaviour of resorptive lesions [Heithersay, 2007]. It has been
suggested that abnormal local pressures, such as ectopic position of the
tooth bud, may be a stimulating factor [Seow, 1999b].

It had been assumed that PEIR would progress unless intervention
occurs but the various case reports showed significant variation in the
clinical course for PEIR lesions. The progress of the lesion is slow
before the tooth erupts into the oral cavity, although some lesions do
progress rapidly [Holan et al., 1994; Seow, 1998; Klambani et al., 2005;
Hata et al., 2007]. A number of cases suggest surgical exposure of the
unerupted tooth to restore the lesion to avoid continued destruction of
coronal structure. There are no reports of progression when the lesions
have been removed and restored [Table 3]. When the affected tooth
erupts, it is assumed that microorganisms may ingress through
microscopic external enamel openings into the resorbed cavity to cause
further breakdown, so that a large carious lesion results [McNamara et
al., 1997; Seow, 2003]. The majority of case reports suggest that the
affected teeth remain asymptomatic as the lesion rarely extends into the
pulp.

No gender or racial predilection has been reported but Nik and
Rahman [2003] reported a far greater subject prevalence in Malaysian
subjects than in other populations [Table 1]. No systemic factors seem
to predispose a child to PEIR [Seow, 2000]. The only significant
association reported to date is the high prevalence of ectopically
positioned teeth that are associated with these defects [Seow et al.,
1999a; Ozden and Acikgoz 2009].

Case Reports

Case 1: An intra-coronal radiolucency in the unerupted lower right
second premolar was an incidental finding on OPT of a 10 year old girl
(Figure. 1a). The tooth was monitored radiographically prior to and
during eruption. The lesion did not increase in size and there was
continued root development (Figure 1b). The tooth erupted without
incident. It was clinically sound, asymptomatic, with a slight distal
rotation (Figure 1c). There had been no increase in size of the lesion
over time. The tooth was anaesthetised and isolated under rubber dam.
Cavity preparation in the mesio-occlusal aspect of the tooth revealed an
empty space, the base of which was filled with a soft reddish material
(Figure 1d). This was removed with a spoon excavator. The tooth was
restored with an indirect pulp cap, resin modified glass ionomer base
and composite resin, and a fissure sealant was placed in the distal pit
(Figure 1e).

Root development continued to completion (Figure 1f) and the tooth
remained asymptomatic and retained vitality. Histological examination
was inconclusive due to small sample size and contamination of the
sample with oral bacteria.

[FIGURE 1 OMITTED]

Case 2: An intra-coronal radiolucency in the partially erupted
lower right first permanent molar was noted on baseline bitewing
radiographs of a six-year-old girl (Figure 2a). The lesion was monitored
during eruption and the occlusal surface was macroscopically intact. The
tooth was fissure sealed upon eruption with RMGIC and subsequently with
a resin sealant (Figure 2b). A conservative approach was taken and the
lesion was monitored annually. The lesion did not increase in size and
the sealant was intact (Figure 2c). At age 11 years (5 years following
diagnosis) the disto-lingual cusp overlying the PEIR lesion fractured
and the tooth was restored using a preformed metal crown. There was no
evidence of caries. The tooth remained vital and asymptomatic.

[FIGURE 2 OMITTED]

Case 3: A 12-year-old girl was referred by her orthodontist for
restoration of the mandibular left second permanent molar. The left
first permanent molar had been extracted previously as part of the
orthodontic treatment plan and cavitation in the occlusal surface was
noted when the tooth was partially erupted. The orthodontist attempted
to extrude the tooth to facilitate restoration. Clinically there was
extensive occlusal destruction, with a large pulp polyp. The tooth had
an unusual radiographic appearance (Figure 3a). A previous OPT revealed
that an intra-coronal radiolucency was present in the second molar at
least one year prior to its eruption and prior to the extraction of the
first permanent molar (Figure 3b). The second molar was anaesthetised
and isolated under rubber dam. Following removal of the soft tissue
mass, the remaining enamel shell was deemed unrestoreable and the tooth
was extracted. The tooth and associated soft tissue were sent for
histopathological analysis.

Histologically there was a normal amelodentinal junction and enamel
matrix. Irregular resorption was present on the pulpal surface with
osteoclast like giant cells and granulation tissue compatible with PEIR
(Figure 3c). The failure to detect PEIR in the second molar prior to the
extraction of the first permanent molar has complicated the orthodontic
treatment plan.

[FIGURE 3 OMITTED]

Discussion

Radiographs are usually taken in children for caries detection and
for orthodontic treatment planning. Although the prevalence rates have
been reported using bitewing radiographs and OPTs, PEIR can be detected
using either radiograph. All radiographs must be examined completely for
incidental findings. There is a high prevalence of ectopically
positioned teeth affected by PEIR or being adjacent to teeth with PEIR
[Seow et al., 1999a; Ozden and Acikgoz 2009]. Good quality radiographs
that include the maximum information may result in early diagnosis of
PEIR. Radiographs of these three cases were examined and PEIR affected a
single tooth only with no anomalies associated with these affected
teeth.

The aetiology of these lesions is as yet, not fully understood and
more research is needed in this area. However, it appears that
retrospective diagnosis is common and gaining adequate numbers of teeth
or tissue for investigation may be difficult. Regardless of the cause of
the lesion, the clinician must choose the treatment modality that is
most suitable for the particular clinical presentation. Historically,
the dental literature recommended immediate surgical intervention and
restoration to limit the extent of the resorptive lesion and prevent its
progression into the dental pulp. Tooth resorption can be continuous and
potentially aggressive [Heithersay, 2007]. However, not all lesions
progress and if progression is not detectable radiographically,
restorative treatment can be delayed until the tooth is fully erupted.
This approach was adopted in Case 1 where the lesion was removed and the
tooth restored upon eruption. Similar to many other reports, there was
no communication with the pulp chamber and the integrity of the pulp was
maintained. In Case 2 of this series, restorative treatment was deferred
for 5 years as radiographically the lesion did not progress and
clinically the tooth was intact in a caries free dentition. Moskovitz
and Holan [2004] previously reported a non-progressive lesion in an
unerupted second permanent molar, however they restored the lesions on
eruption of the tooth similar to Case 1.

Case 2 illustrates an active decision not to restore a
non-progressive lesion in a tooth following eruption. The majority of
case reports suggest that the affected teeth remain asymptomatic as the
lesion rarely extends into the pulp. The controversy therefore is when
or if the clinician should intervene? There is no consensus in the
various case reports as many clinical variables can determine the
outcome. There are conflicting reports on whether these lesions are
progressive or non-progressive. Case 2 is the first report of long-term
evaluation without intervention to restore the lesion upon eruption.
Radiographically the lesion did not progress in size radiographically
but the undermined cusp fractured after 5 years. It could be argued that
radiographs are an insensitive way to evaluate any dimensional change in
a three dimensional lesion. There are no case reports of progression or
reactivation following removal of the PEIR lesion and its replacement
with a restoration (Table 3). In some cases, apexogenesis or pulpectomy
has been provided either electively or following exposure with a
successful outcome [Ignelzi et al.,1990; O'Neal et al., 1997]. This
was the intended treatment for Case 3, however the extent of coronal
resorption was too great to allow restorative treatment.

The management of teeth with PEIR should be centered on early
diagnosis and treatment at an appropriate time. If a relatively small
lesion is detected or if a tooth is close to eruption, it may be
monitored carefully until the tooth erupts into the oral cavity. Early
intervention would be appropriate, using restoration of lesion for
patients at high risk for caries, those with poor attendance record or
those with limited co-operation. Radiographic monitoring of the lesion
size will direct if intervention pre-eruptively may be necessary.

When lesions are large, appear to be encroaching on the pulp or
where the lesion appears to be enlarging, it may be appropriate to
surgically expose the tooth in order to allow curettage and restoration.
Where there has been pulp involvement without infection, the pulp has
remained vital and further root development occurred [Ignelzi et al.,
1990; O'Neal et al., 1997]. As mentioned previously, recurrence of
the resorption after curettage of the lesion has not been reported in
the literature, so that restoration of the lesion is a valid treatment
option.

The cases presented add to the treatment modalities that may be
offered when PEIR is diagnosed. Fewer than 100 cases have been reported
in the literature yet the reported prevalence suggests that this lesion
is not uncommon. Teeth affected by or adjacent to teeth with PEIR
lesions may be ectopically positioned. All clinicians must be able to
differentiate between PEIR and carious lesions and discuss options
appropriate to the patient on an individual level. In two of the cases
the lesions were diagnosed prior to eruption (Cases 1 and 2). Both
lesions were monitored until the teeth involved were fully erupted and
definitive restoration was possible. Neither of the lesions increased in
size nor changed in shape during the monitoring period. This allowed
treatment to be postponed until an appropriate time. The rate of
progression varies and must be monitored. In Case 2, this involved a
period of several years--the occlusal surface of the tooth was protected
with a fissure sealant. In both affected teeth root development
continued to completion and both teeth have retained vitality.

Case 3 was different in that the lesion was diagnosed
post-eruptively and the tooth involved had presented with a large
destructive lesion, similar to that reported by Rankow and co-workers
[Rankow et al., 1986]. The unusual radiographic appearance of the tooth
prompted retrieval of all previous radiographs of the tooth in question.
An OPT showed that an intra-coronal radiolucency had been present in the
second permanent molar at least eighteen months prior to presentation,
while the tooth was unerupted. Unfortunately, the lesion had not been
detected at this stage and extraction of first permanent molars was
planned by the orthodontist. Forced eruption of the tooth to facilitate
restoration was a reasonable option however the extent of the lesion was
too great. In retrospect, the first molar could have been maintained or
surgical exposure and curettage of the PEIR lesion could have been
offered. This case emphasises the importance of assessing all
radiographs including all unerupted teeth in cases where extractions are
planned as part of an orthodontic treatment plan.

Conclusion

A number of treatment options are available if PEIR is diagnosed
either via bitewing radiographs or OPT. PEIR appears to be resorptive in
nature yet the stimulus for this resorption is not known. The location
of the lesion is predictable and it appears that the lesions can be
progressive or non-progressive. The majority of lesions are not
aggressive and can be controlled by curettage and restoration. The risk
of pulp involvement is low. Clinicians must be aware of PEIR and
document the treatment chosen with long term follow-up to support
further investigation into this entity.